Isometric muscle strength is an indicator of self-reported physical functional disability in patients with rheumatoid arthritis

The objective of our study was to examine (1) whether isometric musclestrength contributes to the explanation of the physical functionaldisability of a rheumatoid arthritis (RA) patient population afteraccounting for other disease parameters and demographic variables and (2)whether change in isometric muscle strength is an indicator of change inphysical functional disability. Sixty-five consecutive patients fulfillingthe American Rheumatism Association 1987 revised criteria for RA wereincluded in the study. Isometric muscle strength was measured with avalidated Muscle Strength Index (MSI) calculated as the mean score ofstandardized isometric extension and flexion strength of the knee and elbowjoints. Physical functional disability was measured with the physicaldimension of the Health Assessment Questionnaire (HAQ). For 56 patients, wecould obtain 1 yr follow-up data. Cross-sectionally, there was asignificant correlation (r = - 0.51, P < 0.01) between the MSI and theHAQ. Muscle strength remained a significant determinant of the HAQ inmultivariate analysis accounting for disease and demographic variables.Longitudinally, change in MSI explained additional variance of change inHAQ after accounting for change in pain, the most important correlate ofchange in HAQ.